They're thinking about it. They have to be thinking about it. How could they not be thinking about it?

These are the Washington Capitals. This is the franchise that has lost 10 postseason series in which it held a two-game lead, including one last year. No NHL franchise has lost more, and the Capitals have been around only since 1974. They're younger than Jaromir Jagr. And here they are, having won the first three games of this first-round series against the Flyers, now facing a Game 6 at the Wells Fargo Center on Sunday, and they wouldn't be human, and they certainly wouldn't be Washington Capitals, if they weren't thinking about that history, and if it weren't weighing on them a bit.

"I don't think this team has any playoff history. It's our first playoffs together," defenseman Karl Alzner said Friday night after the Flyers' improbable, 2-0 victory in Game 5. "Sorry to be cheeky, but that's the truth, I think."

Actually, you could tell from the way they talked that they're thinking about it, mostly because, like Alzner, they tried so hard to tell everyone that they weren't thinking about it. The lads protest too much, methinks. Listening to their answers after Game 5 was like listening to Walter Sobchak, John Goodman's character in The Big Lebowski, who enjoys finishing his coffee and sitting in a family restaurant while he mumbles agitatedly about finishing his coffee and sitting in a family restaurant.

Someone asked forward Nicklas Backstrom, for instance, what Backstrom would tell those fans of the team who are worried because of the Capitals' playoff history.

"Which history?" Backstrom said.

Everyone knows the history. Backstrom has been a Capital for nine years. He knows all about the organization's past.

"I don't know anything about the past," he said. "I'm looking forward to the next game in Philly on Sunday."

Look, the Capitals could very well blow the Flyers out of the building Sunday. Washington has dominated the last four periods of this series - the third period of Game 4 and the entirety of Game 5 - and Michael Neuvirth's transcendent goaltending has been the only thing standing between the Flyers and the start of summer vacation. Neuvirth has to break at some point, doesn't he? The Capitals are counting on it.

"If we play our game, it's going to go our way sooner or later," Washington goaltender Braden Holtby said. "If we just keep our composure and keep looking forward, there's no way we won't win one of the last two games."

That's how the Capitals ought to be approaching Game 6. But if Neuvirth remains impenetrable, and if the Flyers score the first goal Sunday, how long will it take for the frustration and the pressure to prey on the Capitals' minds? This would not be just another early postseason exit for a franchise accustomed to such results. Not to overstate matters, but if the Flyers were to win this series, it would qualify as both the biggest upset and the greatest comeback in NHL postseason history. If you take all the relevant factors into consideration, it's difficult to reach another conclusion. So let's consider them.

Just four NHL teams - the 2009-10 Flyers among them - have rallied from a three-games-to-none deficit to win a best-of-seven series. But in none of those series was the intrinsic gap between the opponents as wide as it is here. In 1942, the Toronto Maple Leafs beat the Detroit Red Wings in the Stanley Cup Finals. In 1975, when the New York Islanders stunned the Pittsburgh Penguins in the quarterfinal round, the teams had been one point apart in the regular-season standings: The Penguins had 89 points, the Islanders had 88. A similar dynamic was at play in 2010, when the Flyers, with 88 points and seeded seventh in the Eastern Conference, knocked off the Boston Bruins, with 91 points and seeded sixth. And in 2014, the Los Angeles Kings won their second Stanley Cup in three years after their comeback against the San Jose Sharks, even though they had finished behind the Sharks in the Pacific Division.

At its beginning, this Flyers-Capitals series didn't seem a fair fight. The Capitals put up 120 points to win the Presidents' Trophy as the league's best regular-season team. They finished 11 points ahead of any other NHL team and 24 points ahead of the Flyers, who didn't clinch a playoff berth until they won their next-to-last game of the season. The Capitals scored the second-most goals in the league (252) and allowed the second-fewest (193). The Flyers gave up more goals (218) than they scored (214).

The first three games unfolded without a genuine surprise: Capitals, 2-0; Capitals, 4-1; Capitals, 6-1. Only a daily congregant in the Church of the Orange and Black would have given the Flyers a chance then, especially after the way they unraveled over the final 15 minutes of Game 3. Yet here they are, sitting where the catbird usually does. If they lose Sunday, well, they gave it a good effort; they rallied admirably; and, in the end, the better, more talented team won. But if the Capitals lose Game 6, that history will be nothing but a boulder on their backs in Game 7. They'd be thinking about it, every one of them.

Sorry to be cheeky, but that's the truth, I think.

msielski@phillynews.com

@MikeSielski